The California Nurses Association said the nurses are calling on hospitals to increase staffing levels and take steps to retain experienced workers. They are also demanding policies that give them a stronger voice in patient care.

Tessie Costales, a registered nurse for 29 years, estimated there were a few hundred marchers outside the Los Angeles medical center.

“Short staffing means high risk for patients’ care,” said Costales, 59. “They have to correct this problem.”

Officials at Kaiser and Sutter said backup workers would be used to make sure there is no interruption in care.

“Each of our impacted hospitals has contracted with an agency that provides licensed, experienced registered nurses to fill in for those who choose to strike,” said Dr. Stephen Lockhart, Sutter’s chief medical officer.

The nurses association said the strikers will be joined Friday by nurses from Providence’s Torrance hospital and Providence Saint John’s Health Center in Santa Monica.